With the development of semiconductor manufacturing technology, the application fields for semiconductor devices have increased, so various studies and research have been extensively performed to increase the integration degree of the semiconductor devices. As the integration degree of semiconductor devices has increased, studies have been increasingly pursued to fabricate semiconductor devices in a micro-size based on micro-fabrication processes. In micro-fabrication technology for semiconductor devices, isolation layer diminishing technology for isolating devices from each other to integrate devices is very important.
As a conventional isolation technology, the LOCOS (local oxidation of silicon) technology forms an isolation layer by selectively growing a thick oxide layer on a semiconductor substrate. However, according to the LOCOS technology, an oxide layer is formed in a region where a lateral diffusion is not required, so that there is limitation to reduce the width of an isolation layer.
Therefore, the LOCOS technology is not applicable for a semiconductor device having a scale of submicron, so a new isolation technology is required.
In this regard, a shallow trench isolation technology has been suggested. According to the shallow trench isolation technology, a shallow trench is formed in a semiconductor device through an etching process, and an insulating material is filled in the shallow trench, thereby reducing the width of the isolation region more than the LOCOS technology.
Such a shallow trench isolation technology is applied to a CMOS image sensor, which is a semiconductor device for converting an optical image into an electric signal. As a photo device is highly integrated, the size of a photodiode used in the CMOS image sensor is also reduced. In this case, the photons injected into neighboring pixels may generate electrons and holes in other pixels while passing through the shallow trench isolation structure, so that the optical device characteristic may be degraded. That is, the dark current and crosstalk may occur in the CMOS image sensor, so there is an endeavor to improve the characteristics of the optical device by solving the dark current and crosstalk.